Through thick and thin: kinematic and chemical components in the solar neighbourhood

By J. Navarro, M. Abadi, K. Venn, Kenneth C. Freeman, B. Anguiano. 2010

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We search for chemically distinct stellar components in the solar neighbourhood using a compilation of published data. Extending earlier work, we show that when the abundances of Fe, α elements and the r-process element Eu are considered together, stars separate neatly into two groups that delineate the traditional thin and thick disc components of the Milky Way. The group akin to the thin disc is traced by stars with [Fe/H] > −0.7 and [α/Fe] < 0.2. The thick disc-like group overlaps the thin disc in [Fe/H] but has higher abundances of α elements and Eu. Stars in the range −1.5 < [Fe/H] < −0.7 with low [α/Fe] ratios, however, seem to belong to a separate, dynamically cold, non-rotating component that we associate with tidal debris. The kinematically hot stellar halo dominates the sample for [Fe/H] < −1.5. These results suggest that it may be possible to define the main dynamical components of the solar neighbourhood using only their chemistry, an approach with a number of interesting consequences. With such definition, the kinematics of thin disc stars is found to be independent of metallicity: their average rotation speed remains roughly constant in the range −0.7 < [Fe/H] < +0.4, a result that argues against radial migration having played a substantial role in the evolution of the thin disc. The velocity dispersion of the thin disc is also independent of [Fe/H], implying that the familiar increase in velocity dispersion with decreasing metallicity is the result of the increasing prevalence of the thick disc at lower metallicities, rather than of the sustained operation of a dynamical heating mechanism. The substantial overlap in [Fe/H] and, likely, stellar age, of the various components might affect other reported trends in the properties of stars in the solar neighbourhood. A purely chemical characterization of these components would enable us to scrutinize these trends critically in order to understand which result from accretion events and which result from secular changes in the properties of the Galaxy.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “Using a compilation of data for stars in the solar neighborhood, Navarro et al. (2011) found a flat MVR for low-[α/Fe] stars, concluding that migration in the solar neighborhood was unimportant.”
THE SPATIAL STRUCTURE OF MONO-ABUNDANCE SUB-POPULATIONS OF THE MILKY WAY DISK (2011, background): “While the stellar content of different survey volumes can (and should) be connected by dynamics, we note that the effective volumes sampled by, e.g., the Fuhrmann (2011) survey and by our analysis differ by a factor of about 105; hence the extrapolation from one to the other is enormous.”
A RADIAL AGE GRADIENT IN THE GEOMETRICALLY THICK DISK OF THE MILKY WAY (2016, background): “…et al. 2003; Adibekyan et al. 2012; Haywood et al. 2013); (3) chemically, as the α-rich sequence in the [α/Fe] versus [Fe/H] plane (Fuhrmann 1998; Navarro et al. 2011; Adibekyan et al. 2012; Bovy et al. 2012); (4) as the old part of the disk (Haywood et al. 2013; Bensby et al. 2014; Xiang et…”
The Milky Way’s stellar disk (2013, background): “…in the immediate Solar neighborhood a number of studies, usually based on the Hipparcos catalog, have revealed quite striking abundance patterns in their samples (especially Bensby et al. 2003; Nordström et al. 2004; Bensby et al. 2005; Feltzing & Bensby 2008; Navarro et al. 2011; Fuhrmann 2011).”
The age structure of stellar populations in the solar vicinity Clues of a two-phase formation history of the Milky Way disk (2013, background): “Note, however, that starting from rather different, opposing assumptions, Navarro et al. (2011) interpreted the absence of a V– [Fe/H] relation in the local thin disk as an absence of migration processes.”
THE EFFECT OF RADIAL MIGRATION ON GALACTIC DISKS (2014, background): “One compelling example involves the origin of the large spread in metallicity of the thin disk, which spans the range −0.7 <[Fe/H]< 0.3 (see, e.g., Navarro et al. 2011, and references therein).”
Exploring the Milky Way stellar disk - A detailed elemental abundance study of 714 F and G dwarf stars in the solar neighbourhood (2013, background): “Recently, Navarro et al. (2011) have argued that it is betterto identify stars with different populations based on their elemental abundances rather than other properties such as kinematics.”
A SPECTROSCOPIC CATALOG OF THE BRIGHTEST (J < 9) M DWARFS IN THE NORTHERN SKY, (2012, background): “…thus weaken the correlation between ζ and Fe/H. Theα/Fe abundance ratio is however relatively small in metal-rich stars of the thin disk (±0.05dex) disk stars, and are found to be significant (±0.2dex) mostly in more metal-poor stars associated with the thick disk and halo (Navarro et al. 2011).”
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient (2016, background): “Therefore, these studies suggest that we should define thick and thin disc stars depending on their chemical properties (e.g. Lee et al. 2011; Navarro et al. 2011), although it requires high-quality high-resolution spectroscopic survey which is observationally quite expensive.”
Thin disc, thick disc and halo in a simulated galaxy (2012, methodology): “In Section 2.2, we follow Navarro et al. (2011) and separate our (analogous) solar neighbourhood stars on the basis of their abundances, and find that such classification results in components that could reasonably be referred to as a thin disc, thick disc and halo/metal weak thick disc (MWTD),…”
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program - Galactic stellar populations and planets (2012, methodology): “…thin disk stars are a purely kinematical approach (e.g. Bensby et al. 2003, hereafter B03, 2005; Reddy et al. 2006), a purely chemical method (e.g. Navarro et al. 2011; Adibekyan et al. 2011), and looking at a combination of kinematics, metallicities, and stellar ages (e.g. Fuhrmann 1998; Haywood…”
Confirming chemical clocks: asteroseismic age dissection of the Milky Way disc(s) (2017, methodology): “…in the solar neighbourhood using chemistry and kinematics (e.g. Fuhrmann 1998; Soubiran, Bienaymé & Siebert 2003; Bensby, Feltzing & Lundström 2003; Navarro et al. 2011; Ramı́rez, Allende Prieto & Lambert 2013; Rojas-Arriagada et al. 2016; Allende Prieto, Kawata & Cropper 2016, just to name a…”
INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS (2013, background): “Kinematic vs. chemical definitions of disk components likely involve significant mixing of the thin and thick populations (e.g., Navarro et al. 2011; Lee et al. 2011).”